1. Field of the Invention
The present invention relates to a passive solar energy system and more particularly to a passive thermal storage system. Specifically, the present invention relates to a system and method for controlling the charging of a thermal storage wall through insolation of solar energy and through the release of thermal energy from the thermal storage wall.
2. Description of the Prior Art
The use of solar insolation for heating buildings of passive solar design has increased significantly in the past several years due to the substantial savings of such systems over heating systems in conventional buildings using fossil fuel energy. Although a number of different and useful techniques have been developed for use in passive solar design to increase the storage of solar radiation during the daylight hours, suitable techniques for regulating the control of this stored solar radiation (in the form of thermal energy) are not truly satisfactory. A common technique for storing solar radiation in the form of thermal energy is to use a masonry, such as brick, concrete, adobe, or stone, or a water wall or cylinder such as what has been commonly termed the Trombe wall. Thermal energy stored in such walls is released by free convection air currents and by thermal radiation.
Conventionally, once a solar passive building is designed and constructed, the thermal behavior of that building is controlled primarily by its external thermal environment. Without using any supplementary or auxiliary heat, the average room temperatures of such solar passive buildings are higher during the day when insolation occurs and lower at night and in the early morning hours. The variations between the high and the low temperatures in each room is a function of the building design and the magnitude of change in weather conditions. Often the difference of variation can be large, such as 15.degree. F. or greater.
Most passive solar buildings are constructed as a single zone wherein the building is typically one room deep with the south end of each room designed to receive solar radiation through typically glass enclosed openings. In such passive building designs, rear or back rooms, behind the first room, cannot be effectively heated by solar radiation. One solution to this problem has been to use free convection in order to transfer heat from the front room or zone to the back room or zone. Free air, however, has a small heat capacity, and difficulties are generally encountered in controlling and setting up suitable convection patterns. Furthermore, heat transferred through the storage walls (i.e., interzonal transfer) is limited since masonry materials are especially poor thermal conductors.
In some techniques, regulation of heat transfer from the storage wall has been accomplished by use of a fan. The use of such a device, however, has limitations. A fan generally helps to improve heat transfer but it cannot provide the additional impedance needed during charging of the thermal walls (i.e., during the day) to prevent overheating of the front room and to improve storage wall performance.
Another technique is to employ the use of an auxiliary heat source to supplement the temperature of the rooms during the night and early morning hours.
Another approach has been to utilize moveable insulation and louver shading devices to provide a degree of passive thermal control. These types of shading devices affect the degree by which the thermal wall is charged by solar insolation. Such techniques, however, do not control the release of thermal energy from the storage wall into the air space of the room. Furthermore, shading devices do not provide directional or graduated control over the discharge of thermal energy and fail to improve interzonal heat transfer from a front room to a back room or improve the heat storage performance of the storage wall itself.